Physiological, immunological, and oxidative stress responses of common carp (Cyprinus carpio) to aniseed oil (Pimpinella anisum) immersion across two life stages

The rapid expansion of aquaculture necessitates safe anesthetics to minimize handling-induced stress. This study evaluates aniseed oil ( Pimpinella anisum ) as an immersion anesthetic for common carp ( Cyprinus carpio ) across two life stages. Fingerlings (55 ± 5 g) and adults (350 ± 20 g) were exposed to concentrations ranging from 40 to 120 mg/L. Physiological, immunological, and oxidative stress biomarkers were assessed ( n = 6/group). While lower concentrations (40–100 mg/L) induced only partial sedation, 120 mg/L reliably achieved rapid deep anesthesia (induction: 0.25 ± 0.03 min in fingerlings; 0.42 ± 0.03 min in adults) with smooth recovery (< 8 min) and 100% survival. Plasma cortisol levels remained within baseline ranges (6.12–14.12 ng/mL) across all groups, indicating minimal HPI axis activation. Hepatic enzymes (ALT, AST) showed no evidence of acute hepatotoxicity at 120 mg/L. Furthermore, fish exposed to 120 mg/L exhibited significantly reduced malondialdehyde (MDA) levels (4.20 ± 0.13 nmol/mL in fingerlings; 4.80 ± 0.13 nmol/mL in adults) and elevated superoxide dismutase (SOD) activity (68.00 ± 1.00 U/mL in fingerlings; 61.00 ± 1.00 U/mL in adults) compared to controls. Plasma immunoglobulin M (IgM) levels were significantly elevated at 120 mg/L, particularly in fingerlings (277.67 ± 4.73 μg/mL), which may reflect an immunomodulatory action. These findings indicate that trans-anethole-rich aniseed oil demonstrates physiological compatibility and may confer antioxidant and immunostimulatory benefits during anesthesia. However, histopathological evaluation of major organs is recommended for tissue-level validation before widespread implementation.